In my mind, this behavior parallels smoking and smokers. Smoking was banned in school, but the smokers could always be found sneaking their habit somewhere on school grounds. Furthermore, all the taxes smokers have endured still do not make it any easier for them to quit. So, to me, it seems a soda tax would not work. However, it turns out I'm wrong. An article in this month's issue (page 25), by the USDA's Economic Research Service (ERS), reports that a tax of at least 20% on sugary beverages, an increase that directly hits consumers, is needed to result in change. Taking various factors into account, the report states consumers would then choose bottled water first, followed by other beverages, such as juice and diet drinks.
Based on this ERS study, the changes would "translate into an average loss per year of 3.8lbs for adults and 4.5lbs for children." Perhaps these figures do not seem like much, but Americans between the ages of 25-55 gain about 1.5lbs per year. Ditching sugary drinks or foods seems like a straightforward, easy way to cut many extra calories, slowing the path to obesity. (Logically, this will only work, if people do not eat extra foods or beverages that will "make up" for the saved calories.)